Method for forming low-k hard film

ABSTRACT

A hard film is formed on an insulation film formed on a semiconductor substrate by vaporizing a silicon-containing hydrocarbon compound to provide a source gas, introducing a reaction gas composed of the source gas and optionally an additive gas such as alcohol to a reaction space of a plasma CVD apparatus, and applying low-frequency RF power and high-frequency RF power. The silicon-containing hydrocarbon compound includes a cyclic Si-containing hydrocarbon compound and/or a linear Si-containing hydrocarbon compound, as a basal structure, with reactive groups for form oligomers using the basal structure. The residence time of the reaction gas in the reaction space is lengthened by reducing the total flow of the reaction gas in such a way as to form a siloxan polymer film with a low dielectric constant.

This is a continuation-in-part of U.S. patent application Ser. No.10/317,239 filed Dec. 11, 2002, which is a continuation-in-part of U.S.patent application Ser. No. 09/827,616 filed Apr. 6, 2001, now U.S. Pat.No. 6,514,880 which is a continuation-in-part of (i) U.S. patentapplication Ser. No. 09/243,156 filed Feb. 2, 1999, now abandoned, whichclaims priority to Japanese patent application No. 37929/1998 filed Feb.5, 1998, (ii) U.S. application Ser. No. 09/326,847 filed Jun. 7, 1999,now U.S. Pat. No. 6,352,945, (iii) U.S. patent application Ser. No.09/326,848 filed Jun. 7, 1999, now U.S. Pat. No. 6,383,955, and (iv)U.S. patent application Ser. No. 09/691,376 filed Oct. 18, 2000, nowU.S. Pat. No. 6,432,846, all of which are incorporated herein byreference in their entirety. This application claims priority to all ofthe foregoing under 35 U.S.C. § 119 and § 120.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a semiconductor technique and moreparticularly to a silicone polymer film used as a low-k (low dielectricconstant) hard film on a semiconductor substrate, which is formed byusing a plasma CVD (chemical vapor deposition) apparatus.

2. Description of the Related Art

Because of the recent rise in requirements for the large-scaleintegration of semiconductor devices, a multi-layered wiring techniqueattracts a great deal of attention. In these multi-layered structures,however, capacitance among individual wires hinders high speedoperations. In order to reduce the capacitance it is necessary to reducerelative dielectric constant of the insulation film. Thus, variousmaterials having a relatively low relative dielectric constant have beendeveloped for insulation films.

Conventional silicon oxide films SiO_(x) are produced by a method inwhich oxygen O₂ or nitrogen oxide N₂O is added as an oxidizing agent toa silicon source gas such as SiH₄ or Si(OC₂H₅)₄ and then processed byheat or plasma energy. Its relative dielectric constant is about 4.0.

Alternatively, a fluorinated amorphous carbon film has been producedfrom C_(x)F_(y)H_(z) as a source gas by a plasma CVD method. Itsrelative dielectric constant ∈ is as low as 2.0–2.4.

Another method to reduce the relative dielectric constant of insulationfilm has been made by using the good stability of Si—O bond. Asilicon-containing organic film is produced from a source gas under lowpressure (1 Torr) by the plasma CVD method. The source gas is made fromP-TMOS (phenyl trimethoxysilane, formula 1), which is a compound ofbenzene and silicon, vaporized by a babbling method. The relativedielectric constant ∈ of this film is as low as 3.1.

A further method uses a porous structure made in the film. An insulationfilm is produced from an inorganic SOG material by a spin-coat method.The relative dielectric constant ∈ of the film is as low as 2.3.

However, the above noted approaches have various disadvantages asdescribed below.

First, the fluorinated amorphous carbon film has lower thermal stability(370° C.), poor adhesion with silicon-containing materials and alsolower mechanical strength. The lower thermal stability leads to damageunder high temperatures such as over 400° C. Poor adhesion may cause thefilm to peel off easily. Further, the lower mechanical strength canjeopardize wiring materials.

Oligomers that are polymerized using P-TMOS molecules do not form alinear structure in the vapor phase, such as a siloxane structure,because the P-TMOS molecule has three O—CH₃ bonds. The oligomers havingno linear structure cannot form a porous structure on a Si substrate,i.e., the density of the deposited film cannot be reduced. As a result,the relative dielectric constant of the film cannot be reduced to adesired degree.

In this regard, the babbling method means a method wherein vapor of aliquid material, which is obtained by having a carrier gas such as argongas pass through the material, is introduced into a reaction chamberwith the carrier gas. This method generally requires a large amount of acarrier gas in order to cause the source gas to flow. As a result, thesource gas cannot stay in the reaction chamber for a sufficient lengthof time to cause polymerization in a vapor phase.

Further, the SOG insulation film of the spin-coat method has a problemin that the material cannot be applied onto the silicon substrate evenlyand another problem in which a cure system after the coating process iscostly.

In view of the above, various techniques of forming low-k silicainsulation films have been developed.

In order to reduce wiring resistance, copper wiring is widely used incombination with low-k silica insulation films. However, copper tends tomigrate or diffuse into the silica insulation films. In order to preventthis problem, a hard film is required between the silica insulation filmand copper wiring. Conventionally, SiC or SiN is mainly used as a hardfilm. However, the dielectric constant of such a hard film is relativelyhigh, and thus when forming the hard film on the silica insulation film,the hard film increases the effective dielectric constant of theintegrated layers of the hard film and the silica insulation film, evenif the dielectric constant of the insulation film is low.Conventionally, as a source gas, 3MS or 4MS is used, and films having adielectric constant of less than 4.0 have not been obtained, although ahard film having a low dielectric constant is in demand for reducing theeffective dielectric constant at the low-k insulation film.

Therefore, a principal object of this invention is to provide a methodfor forming an improved hard film which has a low dielectric constant.

Further, properties such as fine structures, barrier effect againstcopper, and controlling film stress are required for hard films. Anotherobject of this invention is to provide a method for forming a hard filmthat has a low dielectric constant, fine structures, and appropriatelevels of film stress.

A further object of this invention is to provide a method for forming ahard film that has good mechanical strength.

A still further object of this invention is to provide a method foreffectively forming a hard film without requiring complicated processes.

SUMMARY OF THE INVENTION

One aspect of this invention may involve a method for forming aninsulation film on a semiconductor substrate by using a plasma CVDapparatus including a reaction chamber, which method comprises a step ofdirectly vaporizing a silicon-containing hydrocarbon compound expressedby the general formula Si_(α)O_(β)C_(x)H_(y) (α,β, x, and y areintegers) and then introducing it to the reaction chamber of the plasmaCVD apparatus, a step of introducing an additive gas, the flow volume ofwhich is substantially reduced, into the reaction chamber and also astep of forming an insulation film on a semiconductor substrate byplasma polymerization reaction wherein mixed gases made from thevaporized silicon-containing hydrocarbon compound as a source gas andthe additive gas are used as a reaction gas. It is a remarkable featurethat the reduction of the additive gas flow also results in asubstantial reduction of the total flow of the reaction gas. Accordingto the present invention, a silicone polymer film having a microporeporous structure with low dielectric constant can be produced.

The present invention is drawn to a hard film that may be formed on theabove insulation film on a semiconductor substrate, that may be incontact with copper wiring, and that may have characteristics describedabove.

In embodiments of the present invention, by using an organo silicon as asource gas which flows at a decreased flow rate to lengthen theresidence time (defined below), plasma polymerization is carried out ina gaseous phase in a reaction chamber to form a hard film having finestructures, and by applying low-frequency RF power, film stress can becontrolled, thereby forming a hard film having a low dielectric constant(e.g., 3.5 or lower). Further, by adding an additive gas, hardness ofthe hard film can be improved.

For purposes of summarizing the invention and the advantages achievedover the prior art, certain objects and advantages of the invention havebeen described above. Of course, it is to be understood that notnecessarily all such objects or advantages may be achieved in accordancewith any particular embodiment of the invention. Thus, for example,those skilled in the art will recognize that the invention may beembodied or carried out in a manner that achieves or optimizes oneadvantage or group of advantages as taught herein without necessarilyachieving other objects or advantages as may be taught or suggestedherein.

Further aspects, features and advantages of this invention will becomeapparent from the detailed description of the preferred embodimentswhich follow.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described withreference to the drawings of preferred embodiments which are intended toillustrate and not to limit the invention.

FIG. 1 is a schematic diagram illustrating a plasma CVD apparatus usableforming a hard film according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In an embodiment of the present invention, a hard film may be formed ona low-k insulation film formed by the methods described below. A hardfilm may be formed using the same source gas as those used for forming alow-k insulation film in an embodiment. In that case, the insulationfilm and the hard film can continuously be formed using the sameequipment, thereby eliminating particle contamination problems andincreasing productivity.

Silica insulation films can be formed by a method comprising the stepsof: (i) vaporizing a silicon-containing hydrocarbon compound to providea source gas; (ii) introducing the source gas into a reaction space forplasma CVD processing wherein a semiconductor substrate is placed; (iii)optionally introducing an additive gas selected from the groupconsisting of an inert gas and an oxidizing gas, said oxidizing gasbeing used in an amount less than the source gas, said source gas andsaid additive gas constituting a reaction gas; and (iv) forming aninsulation film on the semiconductor substrate by activating plasmapolymerization reaction in the reaction space, wherein the plasmapolymerization reaction is activated while controlling the flow of thereaction gas to lengthen a residence time, Rt, of the reaction gas inthe reaction space, wherein 100 msec≦Rt,Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r _(w) ² d/F

-   -   wherein Pr: reaction space pressure (Pa); Ps: standard        atmospheric pressure (Pa); Tr: average temperature of the        reaction (K); Ts: standard temperature (K); r_(w): radius of the        silicon substrate (m); d: space between the silicon substrate        and the upper electrode (m); F: total flow volume of the        reaction gas (sccm).

In the above, the average temperature of the reaction (Tr) is theaverage temperature of the reaction gas at the substrate, which can bedetermined by measuring the temperature of the susceptor. The reactiongas comprises a source gas (i.e., material gas or precursor gas) and anadditive gas (e.g., a carrier gas, an oxidizing gas, a plasmastabilizing gas, etc.). If no additive gas is used, the source gasitself corresponds to the reaction gas.

In the above, the silicon-containing hydrocarbon compound expressed asthe general formula Si_(α)O_(β)C_(x)H_(y) (α, β, x, and y are integers)can be any suitable compounds having structures accomplishingpolymerization or oligomerization of the basal structures of thecompounds under prolonged residence time conditions. The basal structureincludes, but is not limited to, (i) a cyclic Si-containing hydrocarboncompound which may preferably have the formula Si_(n)O_(n)R_(2n−m)wherein n is an integer of 3–6, m represents the number of a unsaturatedbond between Si and C and is an integer of 1–6 (m≦n), and R is C₁₋₆saturated or unsaturated hydrocarbon attached to Si, and (ii) a linearSi-containing hydrocarbon compound which may preferably have the formulaSi_(α)O_(α−1)R_(2α−β+2)X_(β) wherein α and β are integers of 1–3, R isC₁₋₆ hydrocarbon attached to Si, and X is a reactive group. In anembodiment, the formula is Si_(α)O_(α−1)R_(2α−β+2)(OC_(n)H_(2n+1))_(β)wherein α is an integer of 1–3, β is 0, 1, or 2, n is an integer of 1–3,and R is C₁₋₆ hydrocarbon attached to Si.

Reactive groups which form oligomers using the basal structures include,but are not limited to, alkoxy group such as —O—CH₃, unsaturatedhydrocarbon such as —CH═CH₃, amino group such as —NH₂, and acid radicalsuch as carboxylic radical —COOH and acetoxyl group —OCOCH₃. Thereactive group(s) and the basal structure can be included in a singlecompound or different compounds. That is, as long as the reactivegroup(s) and the basal structure exist and forms oligomers, compoundscan be used singly or in any combination.

For example, the silicon-containing hydrocarbon can be a mixture of acyclosiloxan compound (precursor 1) and an unsaturatedhydrocarbon-containing compound (precursor 2). By oligomerization ofprecursor 1 using precursor 2, wherein precursor 1 is linked to eachother using vinyl groups of precursor 2, a film comprised of oligomerscan be formed as described earlier. This film has a low dielectricconstant.

In the above, any suitable cyclosiloxan compound can be used, but thecyclosiloxan compound may preferably have the formulaSi_(n)O_(n)R_(2n−m) wherein n is an integer of 3–6, m represents thenumber of a unsaturated bond between Si and C and is an integer of 1–6(m≦n), and R is C₁₋₆ saturated or unsaturated hydrocarbon attached toSi. The compound has the structure —(SiR_(2−m/n)O)_(n)— and may includehexamethylcyclotrisiloxane

and octamethylcyclotetrasiloxane (OMCTS).

In the above, the unsaturated hydrocarbon-containing compound has atleast one vinyl group. Such a unsaturated hydrocarbon may be selectedfrom the group consisting of compounds of the formula R¹ _(y)Si_(x)R²_(2x−y+2) and compounds of the formula C_(n)H_(2(n−m)+2), wherein R¹ isC₁₋₆ unsaturated hydrocarbon attached to Si, R² is C₁₋₆ saturatedhydrocarbon attached to Si, x is an integer of 1–4, y is an integer of1–2, n is an integer of 1–6, and m represents the number of unsaturatedcarbon bonds and is an integer of 1–5 (n≧m). The above unsaturatedhydrocarbon includes, but are not limited to, unsaturatedhydrocarbon-containing organosilicon such as (CH₃)₂Si(C₂H₃)₂,(C₂H₃)₂SiH₂, (C₆H₅)₂SiH₂, (C₆H₅)SiH₃, (C₆H₅)Si(CH₃)₃, (C₆H₅)₂Si(CH₃)₂,and (C₆H₅)₂Si(OCH₃) ₂, and unsaturated hydrocarbon compounds such asC₂H₄, C₃H₄, C₃H₆, C₄H₈, C₃H₅(CH₃), and C₃H₄(CH₃)₂. The flow ratio ofprecursor 1 (sccm) to precursor 2 (sccm) may be in the range of 0.1 to10 (including 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 5, and a range of anytwo of the foregoing such as a range of 0.5 to 2).

In the above, oligomerization of the cyclosiloxan compound can beperformed with the reactive groups in a vaporous phase, therebydepositing an insulation film comprised of oligomers of the cyclosiloxancompound. According to the above embodiments, the insulation film canhave a dielectric constant of 2.7 or less preferably 2.4 or less.

In another embodiment, the aforesaid basal structure and the reactivegroup(s) are included in a single compound. For example, in the generalformula (Si_(n)O_(n)R_(2n−m))X_(m), wherein X is —O—C_(p)H_(2p+1)wherein p is an integer of 1–4 (preferably 1 or 2) such as —O—CH₃, or—C_(z)H_(2(z−w)+2) wherein z is an integer of 1–4 (preferably 1 or 2),and w represents the number of unsaturated carbon bonds and is aninteger of 1–3 (preferably 1) such as —CH═CH₃. These compounds include1,3,5-trimethyl-1,3,5-trimethoxycyclotrisiloxane

and 1,3,5-trimethyl-1,3,5-trivinyilycyclotrisiloxane.

In the above, oligomerization of the cyclosiloxan compound can beperformed using their reactive groups in a vaporous phase, therebydepositing an insulation film comprised of oligomers of the cyclosiloxancompound. According to the above embodiments, the insulation film canhave a dielectric constant of 2.7 or less preferably 2.4 or less.

In still another embodiment, the silicon-containing hydrocarbon compoundmay have, as the basal structure, a linear siloxan compound which maypreferably have the formula (Si_(α)O_(α−1)R_(2α−β+2))X_(β) or acyclo-siloxan compound which may preferably have the formula(Si_(n)O_(n)R_(2n−m))X_(m), wherein X is a reactive group including, butnot limited to, alkoxy group such as —O—CH₃, an amino group such as—NH₂, and an acid radical such as carboxylic radical —COOH and acetoxylgroup —OCOCH₃. These compounds includes H₂N—Si(CH₃)₂—NH₂ andCH₃OCO—Si(CH₃)₂—OCOCH₃. In the above, if the amino group-containingcompound and the acid radical-containing compound are mixed,polymerization can be enhanced by acid-alkali reaction.

In the above, the reactive groups are attached to the basal structure ina single compound, but the reactive groups and the basal structure canbe different compounds wherein a reactive group gas is separately addedto a basal structure compound to cause oligomization by acid-alkalireaction. For example, the reactive group gas can be any suitable gasincluding N such as dimethylamine ((CH₃)₂NH), N,N-dimethylhydrazine((CH₃)₂NNH₂), ethylazide (C₂H₅N₃), methylamine (CH₃NH₂), andmethylhydrazine (CH₃NHNH₂).

A film formed from a precursor having an amino group and/or an acidradical can suitably be used in formation of a wiring structure. When adevice uses a low dielectric constant film, a resist is applied on a lowdielectric constant film which is then subjected to patterning andetching. Thereafter, the remaining resist is removed and washed out witha chemical solution. In addition to a resist, a sacrificial film may beapplied on the low dielectric film, which may also be removed with achemical solution simultaneously with the resist. The resist and thesacrificial film are organic, and thus their characteristics are similarto those of a low dielectric film (e.g., k<3) which often containsorganic materials. Thus, a chemical solution used for removing a resistand/or a sacrificial film may dissolve the low dielectric film.Accordingly, if a strong chemical solution is used in order to increasethe removal of the resist and/or sacrificial film, it is difficult toprotect the low dielectric film. Many chemical solutions are alkali oracidic. Thus, by rendering the low dielectric film the oppositecharacteristic, i.e., acidic against an alkali solution and alkaliagainst an acidic solution, decomposition of the low dielectric film caneffectively be prevented and protected. This is an example of effectiveuse of a film formed using a precursor having an amino group and/or acidradical as described above.

In the above, oligomerization of the cyclosiloxan compound can beperformed with the reactive groups in a vaporous phase, therebydepositing an insulation film comprised of oligomers of the cyclosiloxancompound. According to the above embodiments, the insulation film canhave a dielectric constant of 2.7 or less. preferably 2.4 or less.

Additionally, all of the aforesaid compounds and the reactive groups canbe used singly or in a combination of at least two of any compoundsand/or at least two of any reactive groups.

Compounds which can be mixed include a compound having at least one Si—Obond, two or less O—C_(n)H_(2n+1) bonds and at least two hydrocarbonradicals bonded with silicon (Si). A preferable silicon-containinghydrocarbon compound has formula:Si_(α)O_(α−1)R_(2α−β+2)(OC_(n)H_(2n+1))_(β)

wherein α is an integer of 1–3, β is 0, 1, or 2, n is an integer of 1–3,and R is C₁₋₆ hydrocarbon attached to Si.

More specifically, the silicon-containing hydrocarbon compound includesat least one species of the compound expressed by the chemical formula(2) as follows:

wherein R1 and R2 are one of CH₃, C₂H₃, C₂H₅, C₃H₇ and C₆H₅, and m and nare any integer.

Except for the species indicated above, the silicon-containinghydrocarbon compound can include at least one species of the compoundexpressed by the chemical formula (3) as follows:

wherein R1, R2 and R3 are one of CH₃, C₂H₃, C₂H₅, C₃H₇ and C₆H₅, and nis any integer.

Except for those species indicated above, the silicon-containinghydrocarbon compound can include at least one species of the compoundexpressed by the chemical formula (4) as follows:

wherein R1, R2, R3 and R4 are one of CH₃, C₂H₃, C₂H₅, C₃H₇ and C₆H₅, andm and n are any integer.

Further, except for those species indicated above, thesilicon-containing hydrocarbon compound can include at least one speciesof the compound expressed by the chemical formula (5) as follows:

wherein R1, R2, R3, R4, R5 and R6 are one of CH₃, C₂H₃, C₂H₅, C₃H₇ andC₆H₅, and the additive gases are argon (Ar), Helium (He) and eithernitrogen oxide (N₂O) or oxygen (O₂).

Furthermore, except for those species indicated above, thesilicon-containing hydrocarbon compound can include at least one speciesof the compound expressed by the chemical formula (6) as follows:

wherein R1, R2, R3 and R4 are one of CH₃, C₂H₃, C₂H₅, C₃H₇ and C₆H₅, andthe additive gases are argon (Ar), Helium (He) and either nitrogen oxide(N₂O) or oxygen (O₂).

Still further, the source gas can include at least one of saidsilicon-containing hydrocarbon compounds indicated above.

In accordance with another aspect, an insulation film is formed on asubstrate and the film is polymerized with plasma energy in a plasma CVDapparatus by using a source gas including a silicon-containinghydrocarbon compound expressed by formula 2.

Additionally, the insulation film is formed on a substrate and the filmis polymerized with plasma energy in a plasma CVD apparatus by using asource gas including a silicon-containing hydrocarbon compound expressedby formula 3.

Further, the insulation film is formed on a substrate and the film ispolymerized with plasma energy in a plasma CVD apparatus by using asource gas including a silicon-containing hydrocarbon compound expressedby formula 4.

Furthermore, the insulation film is formed on a substrate and the filmis polymerized with plasma energy in a plasma CVD apparatus by using asource gas including a silicon-containing hydrocarbon compound expressedby formula 5.

Still further, the insulation film is formed on a substrate and the filmis polymerized with plasma energy in a plasma CVD apparatus by using asource gas including a silicon-containing hydrocarbon compound expressedby formula 6.

In accordance with a further aspect, a material for forming aninsulation film is supplied in a vapor phase in the vicinity of asubstrate and is treated in a plasma CVD apparatus to form theinsulation film on the substrate by chemical reaction, and the materialis further expressed by formula 2.

Additionally, a material for forming an insulation film is supplied in avapor phase in the vicinity of a substrate and is treated in a plasmaCVD apparatus to form the insulation film on the substrate by chemicalreaction, and the material is further expressed by formula 3.

Further, a material for forming an insulation film is supplied in avapor phase in the vicinity of a substrate and is treated in a plasmaCVD apparatus to form the insulation film on the substrate by chemicalreaction, and the material is further expressed by formula 4.

Furthermore, a material for forming an insulation film is supplied in avapor phase with either nitrogen oxide (N₂O) or oxygen (O₂) as anoxidizing agent in the vicinity of a substrate and is treated in aplasma CVD apparatus to form said insulation film on said substrate bychemical reaction, and this material can be the compound expressed byformula 5.

Still further, a material for forming an insulation film is supplied ina vapor phase with either nitrogen oxide (N₂O) or oxygen (O₂) as theoxidizing agent in the vicinity of a substrate and is treated in aplasma CVD apparatus to form said insulation film on said substrate bychemical reaction, and this material further can be the compoundexpressed by formula 6.

The residence time of the reaction gas is determined based on thecapacity of the reaction chamber for reaction, the pressure adapted forreaction, and the total flow of the reaction gas. The reaction pressureis normally in the range of 1–10 Torr, preferably 3–7 Torr, so as tomaintain stable plasma. This reaction pressure is relatively high inorder to lengthen the residence time of the reaction gas. The total flowof the reaction gas is important to reducing the relative dielectricconstant of a resulting film. It is not necessary to control the ratioof the source gas to the additive gas. In general, the longer theresidence time, the lower the relative dielectric constant becomes. Thesource gas flow necessary for forming a film depends on the desireddeposition rate and the area of a substrate on which a film is formed.For example, in order to form a film on a substrate [r(radius)=100 mm]at a deposition rate of 300 nm/min, at least 50 sccm of the source gasis expected to be included in the reaction gas. That is approximately1.6×10² sccm per the surface area of the substrate (m²). The total flowcan be defined by residence time (Rt). When Rt is defined describedbelow, a preferred range of Rt is 100 msec≦Rt, more preferably 200msec≦Rt≦5 sec. In a conventional plasma TEOS, Rt is generally in therange of 10–30 msec.Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r _(w) ² d/F

-   -   wherein:    -   Pr: reaction chamber pressure (Pa)    -   Ps: standard atmospheric pressure (Pa)    -   Tr: average temperature of the reaction (K)    -   Ts: standard temperature (K)    -   r_(w): radius of the silicon substrate (m)    -   d: space between the silicon substrate and the upper electrode        (m)    -   F: total flow volume of the reaction gas (sccm)

In the above, the residence time means the average period of time inwhich gas molecules stay in the reaction chamber. The residence time(Rt) can be calculated at Rt=αV/S, wherein V is the capacity of thechamber (cc), S is the volume of the reaction gas (cc/s), and α is acoefficient determined by the shape of the reaction chamber and thepositional relationship between the inlet of gas and the outlet ofexhaust. The space for reaction in the reaction chamber is defined bythe surface of the substrate (πr²) and the space between the upperelectrode and the lower electrode. Considering the gas flow through thespace for reaction, α can be estimated as ½. In the above formula, α is½.

In this method, the source gas is, in short, a silicon-containinghydrocarbon compound including at least one Si—O bond, at most twoO—C_(n)H_(2n+1) bonds and at least two hydrocarbon radicals bonded tothe silicon (Si). Also, this source gas is vaporized by a directvaporization method. The method results in an insulation film having alow relative dielectric constant, high thermal stability and highhumidity-resistance.

More specifically, the source gas vaporized by the direct vaporizationmethod can stay in the plasma for a sufficient length of time. As aresult, a linear polymer can be formed so that a linear polymer havingthe basic structure (formula 7), wherein the “n” is 2 or a greatervalue, forms in a vapor phase. The polymer is then deposited on thesemiconductor substrate and forms an insulation film having a microporeporous structure.

wherein X1 and X2 are O_(n)C_(m)H_(p) wherein n is 0 or 1, m and p areintegers including zero.

The insulation film has a relatively high stability because itsfundamental structure has the Si—O bond having high bonding energytherebetween. Also, its relative dielectric constant is low because ithas a micropore porous structure. Further, the fundamental structure(—SiO—)_(n) has, on both sides, dangling bonds ending with a hydrocarbonradical possessing hydrophobicity, and this property renders thehumidity-resistance. Furthermore, the bond of a hydrocarbon radical andsilicon is generally stable. For instance, both the bond with a methylradical, i.e., Si—CH₃, and bond with benzene, i.e., Si—C₆H₅, have adissociation temperature of 500° C. or higher. Since above semiconductorproduction requires thermal stability to temperatures above 450° C.,that property of the film is advantageous for production ofsemiconductors.

Further aspects, features and advantages will become apparent from thedetailed description of the preferred examples which follows.

FIG. 1 diagrammatically shows a plasma CVD apparatus usable in thisinvention. This apparatus comprises a reaction gas-supplying device 12and a plasma CVD device 1. The reaction gas-supplying device 12comprises plural lines 13, control valves 8 disposed in the lines 13,and gas inlet ports 14, 15 and 16. A flow controller 7 is connected tothe individual control valves 8 for controlling a flow of a source gasof a predetermined volume. A container accommodating liquid reactingmaterial 18 is connected to a vaporizer 17 that directly vaporizesliquid. The plasma CVD device 1 includes a reaction chamber 6, a gasinlet port 5, a susceptor 3 and a heater 2. A circular gas diffusingplate 10 is disposed immediately under the gas inlet port. The gasdiffusing plate 10 has a number of fine openings at its bottom face andcan inject reaction gas to the semiconductor substrate 4 therefrom.There is an exhaust port 11 at the bottom of the reaction chamber 6.This exhaust port 11 is connected to an outer vacuum pump (not shown) sothat the inside of the reaction chamber 6 can be evacuated. Thesusceptor 3 is placed in parallel with and facing the gas diffusingplate 10. The susceptor 3 holds a semiconductor substrate 4 thereon andheats it with the heater 2. The gas inlet port 5 is insulated from thereaction chamber 6 and connected to an outer high frequency power supply9. Alternatively, the susceptor 3 can be connected to the power supply9. Thus, the gas diffusing plate 10 and the susceptor 3 act as a highfrequency electrode and generate a plasma reacting field in proximity tothe surface of the semiconductor substrate 4.

A method for forming an insulation film on a semiconductor substrate byusing the plasma CVD apparatus comprises a step of directly vaporizingsilicon-containing hydrocarbon compounds expressed by the generalformula Si_(α)O_(β)C_(x)H_(y) (α, β, x, and y are integers) and thenintroducing it to the reaction chamber 6 of the plasma CVD device 1, astep of introducing an additive gas, whose flow is substantiallyreduced, into the reaction chamber 6 and also a step of forming aninsulation film on a semiconductor substrate by plasma polymerizationreaction wherein mixed gases, made from the silicon-containinghydrocarbon compound as a source gas and the additive gas, are used as areaction gas. It is a remarkable feature that the reduction of theadditive gas flow also renders a substantial reduction of the total flowof the reaction gas. This feature will be described in more detaillater.

The additive gases used in this embodiment, more specifically, are argongas and helium gas. Argon is principally used for stabilizing plasma,while helium is used for improving uniformity of the plasma and alsouniformity of thickness of the insulation film.

In the method described above, the first step of direct vaporization isa method wherein a liquid material, the flow of which is controlled, isinstantaneously vaporized at a vaporizer that is preheated. This directvaporization method requires no carrier gas such as argon to obtain adesignated amount of the source gas. This differs greatly with thebabbling method. Accordingly, a large amount of argon gas or helium gasis no longer necessary and this reduces the total gas flow of thereaction gas and then lengthens the time in which the source gas staysin the plasma. As a result, sufficient polymerizing reactions occur inthe vapor so that a linear polymer can be formed and a film having amicropore porous structure can be obtained.

In FIG. 1, inert gas supplied through the gas inlet port 14 pushes outthe liquid reacting material 18, which is the silicon-containinghydrocarbon compound, to the control valve 8 through the line 13. Thecontrol valve 8 controls the flow of the liquid reacting material 18with the flow controller 7 so that it does not exceed a predeterminedvolume. The reduced silicon-containing hydrocarbon compound 18 goes tothe vaporizer 17 to be vaporized by the direct vaporization methoddescribed above. Argon and helium are supplied through the inlet ports15 and 16, respectively, and the valve 8 controls the flow volume ofthese gases. The mixture of the source gas and the additive gases, whichis a reaction gas, is then supplied to the inlet port 5 of the plasmaCVD device 1. The space between the gas diffusing plate 10 and thesemiconductor substrate 4, both located inside of the reaction chamber 6which is already evacuated, is charged with high frequency RF voltages,which are preferably 13.4 MHz and 430 kHz, and the space serves as aplasma field. The susceptor 3 continuously heats the semiconductorsubstrate 4 with the heater 2 and maintains the substrate 4 at apredetermined temperature that is desirably 350–450° C. The reaction gassupplied through the fine openings of the gas diffusing plate 10 remainsin the plasma field in proximity to the surface of the semiconductorsubstrate 4 for a predetermined time.

If the residence time is short, a linear polymer cannot be depositedsufficiently so that the film deposited on the substrate does not form amicropore porous structure. Since the residence time is inverselyproportional to the flow volume of the reaction gas, a reduction of theflow volume of the reaction gas can lengthen its residence time.

Extremely reducing the total volume of the reaction gas is effected byreducing the flow volume of the additive gas. As a result, the residencetime of the reaction gas can be lengthened so that a linear polymer isdeposited sufficiently and subsequently an insulation film having amicropore porous structure can be formed.

In order to adjust the reaction in the vapor phase, it is effective toadd a small amount of an inert gas, an oxidizing agent, or a reducingagent to the reaction chamber. Helium (He) and Argon (Ar) are inertgases and have different first ionization energies of 24.56 eV and 15.76eV, respectively. Thus, by adding either He or Ar singly or both incombination in predetermined amounts, the reaction of the source gas inthe vapor phase can be controlled. Molecules of the reaction gas undergopolymerization in the vapor phase, thereby forming oligomers. Theoligomers are expected to have a O:Si ratio of 1:1. However, when theoligomers form a film on the substrate, the oligomers undergo furtherpolymerization, resulting in a higher oxygen ratio. The ratio variesdepending on the relative dielectric constant or other characteristicsof a film formed on the substrate.

The use of an oxidizing agent or a reducing agent is determineddepending on the target relative dielectric constant (3.30 or less,preferably 3.10 or less, more preferably 2.80 or less) of a siliconepolymer film and other characteristics such as stability of dielectricconstant and thermal stability. The O:Si ratio in the source gas is alsoconsidered to select an oxidizing agent or a reducing agent, asdescribed above. Preferably, if the ratio is lower than 3:2, anoxidizing agent is used, whereas if the ratio is higher than 3:2, areducing agent is used. Further, an inert gas such as Ar and He is forcontrolling plasma reaction, but is not indispensable to form a siliconepolymer film. The flow of source gas and the flow of additive gas canalso vary depending on the plasma CVD apparatus. The appropriate flowcan be determined by correlating the relative dielectric constant of thesilicone polymer film with the residence time of the reaction gas(composed of the source gas and the additive gas). The longer theresidence time, the lower the dielectric constant becomes. A reductionrate of dielectric constant per lengthened residence time is changeable,and after a certain residence time, the reduction rate of dielectricconstant significantly increases, i.e., the dielectric constant sharplydrops after a certain residence time of the reaction gas. After thisdielectric constant dropping range, the reduction of dielectric constantslows down. This is very interesting. In the present invention, bylengthening residence time until reaching the dielectric constantdropping range based on a predetermined correlation between thedielectric constant of the film and the residence time of the reactiongas, it is possible to reduce the relative dielectric constant of thesilicone polymer film significantly.

After the insulation film is formed on a semiconductor substrate, a hardfilm is formed according to the present invention.

In an embodiment, the hard film may be form by a method comprising thesteps of: (i) vaporizing a silicon-containing hydrocarbon compound toprovide a source gas, said silicon-containing hydrocarbon compoundcomprising a cyclosiloxan compound and/or a linear siloxan compound, asa basal structure, with reactive groups for forming oligomers using thebasal structure; (ii) introducing the source gas into a reaction spacefor plasma CVD processing wherein a semiconductor substrate on which aninsulation film is formed is placed; and (iii) forming a hard film onthe insulation film by activating plasma polymerization reaction using acombination of low-frequency RF power and high-frequency RF power in thereaction space, wherein the plasma polymerization reaction is activatedwhile controlling the flow of the reaction gas to lengthen a residencetime, Rt (defined above), of the reaction gas in the reaction space,wherein 100 msec≦Rt (including 110, 120, 130, 140, 150, 160, 170, 180,190, 200, and a range including any of the forgoing).

According to the above embodiment, a hard film having fine structurescan be obtained. By applying low-frequency RF power, film stress of thehard film can be controlled. By overlaying low-frequency RF power andhigh-frequency RF power, film stress of a hard film can be shifted on acompressive side, and for example, a stress of +50 MPa can be reduced to−200 MPa. The low-frequency RF power may be 1%–50% of the high-frequencyRF power (including 5%, 10%, 20%, 30%, 40%, 50%, and a range includingany of the forgoing). The low-frequency RF power may have a frequency of2 MHz or less (including 1 MHz, 800 kHz, 600 kHz, 400 kHz, 200 kHz, 100kHz, 50 kHz, and a range including any of the forgoing). High-frequencyRF power has a frequency of greater than 2 MHz.

The source gas (silicon-containing hydrocarbon) can be selected from thesame group as those used for forming an insulation film as describedabove. Further, the method may comprise introducing a carrier gas intothe reaction space when the source gas is introduced. The carrier gasmay be selected from the group consisting of N₂, He, Ne, and Ar. Theflow of the carrier gas can be determined based on the residence time ifthe pressure is known because the volume of the reaction chamber isconstant. For example, in the residence time equation, if Rt≧100 msec,rw=8 inches, d=24 mm, and Pr=533 Pa, then, F≦545 sccm. Thus, if thereaction gas consists of a source gas and a carrier gas, if the flowrate of the source gas is designated, the flow rate of the carrier gascan be calculated accordingly.

In the above, there may be cases where even if film stress isappropriate, sufficient mechanical strength cannot be accomplished. Byfurther introducing an additive gas selected from the group consistingof an oxidizing gas (such as O₂ and CO₂) and a gas of CxHyOz whereinx=0–3, y=2–15, and z=0–7, into the reaction space when the source gas isintroduced, hardness of the hard film can be improved while optimizingfilm stress of a hard film. The flow rate of additive gas may be 0% toabout 80% of the total flow (including 10%, 20%, 30%, 40%, 50%, 60%,70%, and a range including any two of the foregoing). The flow rates ofsource gas, carrier gas, and additive gas can be determined based on theresidence time equation as described above. In an embodiment, the gas ofCxHyOz may be selected from the group consisting of H₂, C₁₋₆ saturatedor unsaturated hydrocarbon (e.g., CH₄, C₂H₆, C₃H₈, C₂H₄, C₃H₆, C₄H₈,C_(n)H_(2n+1) (n=1–5)), C₁₋₆ alkanol (e.g., CH₃CH(OH)CH₂OH,CH₃CH(OH)OCH₃, CH₃CH(OH)CH₂OCH₃), and C₃₋₂₀ ether (e.g., CH₃CH(OH)CH₃).For example, preferably gases include reactive gases such as ethyleneglycol, 1,2-propanediol, isopropyl alcohol (IPA), ethylene, or diethylether, which may cross-link oligomers of silicon-containing hydrocarbon.Further, any suitable alcohol, ether, and/or unsaturated hydrocarbon canbe used, which include an alcohol selected from the group consisting ofC₁₋₆ alkanol and C₄₋₁₂ cycloalkanol, and the unsaturated hydrocarbonselected from the group consisting of C₁₋₆ unsaturated hydrocarbon,C₄₋₁₂ aromatic hydrocarbon unsaturated compounds, and C₄₋₁₂ alicyclichydrocarbon unsaturated compounds. In the foregoing, compounds having ahigher number of carbon atoms include, but are not limited to:1,4-cyclohexane diol (b.p. 150° C./20 mm), 1,2,4-trivinylcyclohexane(b.p. 85–88° C./20 mm), 1,4-cyclohexane dimethanol (b.p. 283° C.), and1,3-cyclopentane diol (80–85° C./0.1 Torr). Further, compounds havingmultiple reactive groups (‘mixed’ functionalities, i.e., unsaturatedhydrocarbon and alcohol functionalities) can also be used ascross-linkers, which include, but are not limited to: C₃₋₂₀ ether suchas ethylene glycol vinyl ether H₂C═CHOCH₂OH (b.p. 143° C.), ethyleneglycol divinyl ether H₂C═CHOCH₂CH₂OCH═CH₂ (b.p. 125–127° C.), and1,4-cyclohexane dimethanol divinyl ether (b.p. 126° C./14 mm)(H₂C═C(OH)—CH₂)₂—(CH₂)₆); and C₅₋₁₂ cycloalkanol vinyl compounds such as1-vinylcyclohexanol (b.p. 74° C./19 mm). Further, as an oxygen-supplyinggas, O₂, NO, O₃, H₂O or N₂O can be included to supply oxygen in thesource gas if sufficient oxygen atoms are not present in thesilicon-containing hydrocarbon compound.

In another aspect of the present invention, a method may comprise thesteps of: (I) forming an insulation film on a semiconductor substrateplaced in a reaction space by plasma polymerization using asilicon-containing hydrocarbon compound; (II) vaporizing asilicon-containing hydrocarbon compound to provide a source gas, saidsilicon-containing hydrocarbon compound comprising a cyclicSi-containing hydrocarbon compound and/or a linear Si-containinghydrocarbon compound, as a basal structure, with reactive groups forforming oligomers using the basal structure; (III) introducing thesource gas into the reaction space; and (IV) forming a hard film on theinsulation film by activating plasma polymerization reaction using acombination of low-frequency RF power and high-frequency RF power in thereaction space, wherein the plasma polymerization reaction is activatedwhile controlling the flow of the reaction gas to lengthen a residencetime, Rt (defined above), of the reaction gas in the reaction space,wherein 100 msec≦Rt.

In the above, the silicon-containing hydrocarbon used for forming thehard film and the silicon-containing hydrocarbon used for forming theinsulation film may have the same chemical formula. By doing this,particle contamination problems can be effectively eliminated.

Further, when the formation of the insulation film and the formation ofthe hard film are conducted continuously in the reaction space,productivity can be significantly improved.

The formation of a hard film can be conducted in accordance with theprocesses of forming an insulation film, including conditions such asconcentration of gases, flow rates, pressure, and temperature.

According to embodiments of the present invention, a hard film may havea dielectric constant of about less than 4, a stress of about 0 to about300 MPa.

EXAMPLE

Experiments were conducted as described below. The results are indicatedin tables below. In these experiments, an ordinary plasma CVD device(EAGLE®-10, ASM Japan K.K.) was used as an experimental device wherein:

-   -   r_(w) (radius of the silicon substrate): 0.1 m    -   d (space between the silicon substrate and the upper electrode):        0.024 m    -   Ps (standard atmospheric pressure): 1.01×10⁵ Pa    -   Ts (standard temperature): 273 K

Example 1

The conditions for forming a hard film are as follows:

-   -   DMDMOS (dimethyl dimethoxysilane): 160 sccm    -   IPA (isopropyl alcohol): 200 sccm    -   He: 50 sccm    -   Pr (reaction chamber pressure): 500 Pa    -   RF power supply (HF: 13.4 MHz): 1600 W    -   RF power supply (LF: 400 kHz): 200 W    -   Tr (average temperature of the reaction): 673 K    -   F (total flow volume of the reaction gas): 410 sccm    -   Rt (residence time; Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r_(w) ²d/F): 119        ms

The hard film was formed on an insulation film which was formed usingthe same Si-containing hydrocarbon compound under the depositionconditions described in U.S. patent application Ser. No. 10/317,239,filed Dec. 11, 2002, the disclosure of which is incorporated byreference. The characteristics of the hard film obtained are as follows,and as can be seen, all of the dielectric constant, stress, Modulus, andhardness of the hard film are satisfactory:

-   -   k (dielectric constant): 3.5    -   Stress: −160 MPa    -   Modulus: 35 GPa    -   Hardness: 4.1 GPa

Example 2

The conditions for forming a hard film are as follows:

-   -   DMDMOS (dimethyl dimethoxysilane): 160 sccm    -   IPA (isopropyl alcohol): 0 sccm    -   He: 150 sccm    -   Pr (reaction chamber pressure): 533 Pa    -   RF power supply (HF: 13.4 MHz): 1400 W    -   RF power supply (LF: 400 kHz): 300 W    -   Tr (average temperature of the reaction): 673 K    -   F (total flow volume of the reaction gas): 310 sccm    -   Rt (residence time; Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r_(w) ²d/F): 168        ms

The hard film was formed on an insulation film which was formed usingthe same Si-containing hydrocarbon compound under the conditionsdescribed in Example 1. The characteristics of the hard film obtainedare as follows, and as can be seen, all of the dielectric constant,stress, Modulus, and hardness of the hard film are satisfactory:

-   -   k (dielectric constant): 3.4    -   Stress: −180 MPa    -   Modulus: 25 GPa    -   Hardness: 3.1 GPa

Example 3

The conditions for forming a hard film are as follows:

-   -   OMCTC (octamethylcyclotetrasiloxane): 160 sccm    -   DVDVS ((CH₃)₂Si(C₂H₃)₂): 80 sccm    -   He: 100 sccm    -   Pr (reaction chamber pressure): 467 Pa    -   RF power supply (HF: 13.4 MHz): 1500 W    -   RF power supply (LF: 400 kHz): 200 W    -   Tr (average temperature of the reaction): 673 K    -   F (total flow volume of the reaction gas): 340 sccm    -   Rt (residence time; Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r_(w) ²d/F): 120        ms

The hard film was formed on an insulation film which was formed usingthe same Si-containing hydrocarbon compounds under the conditionsdescribed in Example 1. The characteristics of the hard film obtainedare as follows, and as can be seen, all of the dielectric constant,stress, Modulus, and hardness of the hard film are satisfactory:

-   -   k (dielectric constant): 3.5    -   Stress: −190 MPa    -   Modulus: 27 GPa    -   Hardness: 3.3 GPa

Example 4

The conditions for forming a hard film are as follows:

-   -   TMTVS ([CH₂═CH(CH₃)SiO]₃): 140 sccm    -   He: 100 sccm    -   Pr (reaction chamber pressure): 360 Pa    -   RF power supply (HF: 13.4 MHz): 200 W    -   RF power supply (LF: 400 kHz): 50 W    -   Tr (average temperature of the reaction): 673 K    -   F (total flow volume of the reaction gas): 340 sccm    -   Rt (residence time; Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r_(w) ²d/F): 149        ms

The hard film was formed on an insulation film which was formed usingthe same Si-containing hydrocarbon compound under the conditionsdescribed in Example 1. The characteristics of the hard film obtainedare as follows, and as can be seen, all of the dielectric constant,stress, Modulus, and hardness of the hard film are satisfactory:

-   -   k (dielectric constant): 3.3    -   Stress: −140 MPa    -   Modulus: 23 GPa    -   Hardness: 2.8 GPa

Although this invention has been described in terms of certain examples,other examples apparent to those of ordinary skill in the art are withinthe scope of this invention. Accordingly, the scope of the invention isintended to be defined only by the claims that follow. The presentinvention includes various embodiments and are not limited to the aboveexamples. The present invention particularly includes, but are notlimited to, the following embodiments, and any combination of theforgoing embodiments and the following embodiments can readily beaccomplished:

1) A method is for forming an insulation film on a semiconductorsubstrate by plasma reaction and comprises the steps of: (i) vaporizinga silicon-containing hydrocarbon compound to provide a source gas; (ii)introducing the source gas into a reaction space for plasma CVDprocessing wherein a semiconductor substrate is placed; (iii) optionallyintroducing an additive gas selected from the group consisting of aninert gas and an oxidizing gas, said oxidizing gas being used in anamount less than the source gas, said source gas and said additive gasconstituting a reaction gas; and (iv) forming an insulation film on thesemiconductor substrate by activating plasma polymerization reaction inthe reaction space, wherein the plasma polymerization reaction isactivated while controlling the flow of the reaction gas to lengthen aresidence time, Rt, of the reaction gas in the reaction space, wherein100 msec≦Rt,Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r _(w) ² d/F

-   -   wherein Pr: reaction space pressure (Pa); Ps: standard        atmospheric pressure (Pa); Tr: average temperature of the        reaction (K); Ts: standard temperature (K); r_(w): radius of the        silicon substrate (m); d: space between the silicon substrate        and the upper electrode (m); F: total flow volume of the        reaction gas (sccm).

In the above, the reaction space should not be limited to a physicallydefined single section, but should include any suitable space for plasmareaction. That is, as one of ordinary skill in the art readilyunderstands, the space is a functionally defined reaction space. Thespace may be comprised of a physically defined single section such asthe interior of a reactor, or physically defined multiple sectionscommunicated with each other for plasma reaction, such as the interiorof a remote plasma chamber and the interior of a reactor. Further, thespace includes the interior of piping connecting multiple sectionsthrough which a reaction gas passes. The interior of the reactorincludes only the space used for plasma reaction. Thus, if only a partof the reactor interior is used for plasma reaction where the reactor iscomposed of multiple sections, only the part used for plasma reactionconstitutes a reaction space. Further, the plasma reaction includes apreliminary reaction for plasma polymerization. For example, upstream ofa reactor, heating a reaction gas (e.g., 150° C. to 500° C., preferably200° C. to 300° C., in a pre-heater chamber), exciting a reaction gas(e.g., in a remote plasma chamber), or mixing an excited additive gasand a source gas (e.g., in a pre-heater chamber) is included in apreliminary reaction.

2) In the method according to Item 1, the source gas and the additivegas are separately introduced into the reaction space. The additive gasand the source gas can be mixed upstream of a reactor and introducedinto the reactor. However, they can be introduced separately, dependingon the configuration of a reactor. As long as the gases are not in areactive state, regardless of whether the additive gas and the sourcegas are mixed or separated, the space where the gases are present doesnot constitute a reaction space. At a point where additive gas and thesource gas are in contact in a reactive state, the reaction spacebegins. The reactive state includes states where the reaction gas isheated or excited, or the excited additive gas and the source gas aremixed, for example.

3) In the method according to Item 1 or 2, the plasma polymerizationreaction comprises exciting the reaction gas and depositing the film onthe substrate. As described above, the plasma polymerization reactionincludes a preliminary reaction such as excitation of the reaction gas.

4) In the method according to any one of Items 1–3, the reaction spacecomprises a space for exciting the reaction gas and a space fordepositing the film. In this embodiment, the reaction gas can be excitedin a remote plasma chamber installed upstream of a reactor, and the filmis deposited on the substrate in the reactor. The source gas and theadditive gas can be introduced into the remote plasma chamber. In thiscase, the reaction space is composed of the interior of the remoteplasma chamber, the interior of the reactor, and the interior of thepiping connecting the remote plasma chamber and the reactor. Because ofusing the interior of the remote plasma chamber, the interior of thereactor can be significantly reduced, and thus, the distance between theupper electrode and the lower electrode can be reduced. This leads tonot only downsizing the reactor, but also uniformly controlling a plasmaover the substrate surface. Any suitable remote plasma chamber and anysuitable operation conditions can be used in the present invention. Forexample, usable are the apparatus and the conditions disclosed in U.S.patent applications Ser. No. 09/511,934 filed Feb. 24, 2000 and Ser. No.09/764,523 filed Jan. 18, 2001, U.S. Pat. No. 5,788,778, and U.S. Pat.No. 5,788,799. The disclosure of each of the above is incorporatedherein by reference in its entirety.

5) In the method according to Item 3 or 4, the excitation of thereaction gas comprises exciting the additive gas and contacting theexcited additive gas and the source gas. The excitation of the reactiongas can be accomplished in the reactor or upstream of the reactor. Asdescribed above, both the source gas and the additive gas can be excitedin a remote plasma chamber. Alternatively, the excitation of thereaction gas can be accomplished by exciting the additive gas in aremote plasma chamber and mixing it with the source gas downstream ofthe remote plasma chamber.

6) In the method according to any one of Items 1–3, the reaction spacecomprises a space for heating the reaction gas and a space for excitingthe reaction gas and depositing the film. In this embodiment, thereaction gas can be heated in a pre-heat chamber installed upstream of areactor, the reaction gas is excited in the reactor, and film isdeposited on the substrate in the reactor. The source gas and theadditive gas can be introduced into the pre-heater chamber. In thiscase, the reaction space is composed of the interior of the pre-heaterchamber, the interior of the reactor, and the interior of the pipingconnecting the pre-heater chamber and the reactor. Because of using theinterior of the pre-heater chamber, the interior of the reactor can besignificantly reduced, and thus, the distance between the upperelectrode and the lower electrode can be reduced. This leads to not onlydownsizing the reactor, but also uniformly controlling a plasma over thesubstrate surface. Any suitable remote plasma chamber and any suitableoperation conditions can be used in the present invention. For example,usable are the apparatus and the conditions disclosed in the aforesaidreferences.

7) In the method according to Item 6, the excitation of the reaction gascomprises exciting the additive gas and contacting the excited additivegas and the source gas. In this embodiment, the additive gas can beexcited in a remote plasma chamber, and the source gas is heated in apre-heater chamber where the excited additive gas and the source gas arein contact, and then the reaction gas flows into the reactor fordeposition of a film. In this case, deposition of unwanted particles ona surface of the remote plasma chamber, which causes a failure ofignition or firing, can effectively be avoided, because only theadditive gas is present in the remote plasma chamber. The source gas ismixed with the excited additive gas downstream of the remote plasmachamber. The reaction space may be composed of the interior from a pointwhere the excited additive gas and the source gas meet to an entrance tothe reactor, and the interior of the reactor.

8) In the method according to any one of Items 1–7, the additive gas canbe selected from the group consisting of nitrogen, argon, helium, andoxygen, but should not be limited thereto.

9) In the method according to any one of Items 1–8, the plasmapolymerization reaction is conducted at a temperature of 350–450° C.However, the suitable temperature varies depending on the type of sourcegas, and one of ordinary skill in the art could readily select thetemperature. In the present invention, polymerization includes anypolymerization of two or more units or monomers, includingoligomerization.

10) In the method according to any one of Items 1–9, the formation ofthe insulation film is conducted while maintaining a gas diffusing plateat a temperature of 150° C. or higher (e.g., 150° C. to 500° C.,preferably 200° C. to 300° C.), through which the reaction gas flowsinto the reaction space, so that the reaction is promoted. In the above,the gas diffusing plate (or showerhead) may be equipped with atemperature control device to control the temperature. Conventionally,the temperature of the showerhead is not positively controlled and isnormally 140° C. or lower when the temperature of the reaction space is350–450° C., for example.

11) In the method according to any one of Items 1–10, the residence timeis determined by correlating the dielectric constant with the residencetime. This embodiment has been described earlier. The followingembodiments also have been described earlier:

12) In the method according to any one of Items 1–11, the flow of thereaction gas is controlled to render the relative dielectric constant ofthe insulation film lower than 3.10.

13) In the method according to any one of Items 1–12, Rt is no less than165 msec or 200 msec.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. Therefore, it should be clearly understood thatthe forms of the present invention are illustrative only and are notintended to limit the scope of the present invention.

1. A method for forming a hard film on an insulation film formed on asemiconductor substrate by plasma reaction, comprising the steps of:vaporizing a silicon-containing hydrocarbon compound to provide a sourcegas, said silicon-containing hydrocarbon compound comprising a cyclicSi-containing hydrocarbon compound and/or a linear Si-containinghydrocarbon compound, as a basal structure, with reactive groups forforming oligomers using the basal structure; introducing a reaction gascomprising the source gas and a carrier gas into a reaction space forplasma CVD processing wherein a semiconductor substrate on which aninsulation film is formed is placed; and forming a hard film on theinsulation film by activating plasma polymerization reaction using acombination of low-frequency RF power and high-frequency RF power in thereaction space, wherein the plasma polymerization reaction is activatedwhile controlling the flow of the reaction gas to lengthen a residencetime, Rt, of the reaction gas in the reaction space, wherein 100msec≦Rt,Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r _(w) ² d/F wherein: Pr: reaction spacepressure (Pa) Ps: standard atmospheric pressure (Pa) Tr: averagetemperature of the reaction (K) Ts: standard temperature (K) r_(w):radius of the silicon substrate (m) d: space between the siliconsubstrate and the upper electrode (m) F: total flow volume of thereaction gas (sccm).
 2. The method according to claim 1, wherein saidreactive group is selected from the group consisting of alkoxy group,vinyl group, amino group, and acid radical.
 3. The method according toclaim 1, wherein said silicon-containing hydrocarbon is a mixture of acyclosiloxan compound and an unsaturated hydrocarbon-containingcompound.
 4. The method according to claim 3, wherein the cyclosiloxancompound has the formula Si_(n)O_(n)R_(2n−m), wherein n is an integer of3–6, m represents the number of a unsaturated bond between Si and C andis an integer of 1–6 (m≦n), and R is C₁₋₆ saturated or unsaturatedhydrocarbon attached to Si.
 5. The method according to claim 3, whereinthe unsaturated hydrocarbon-containing compound has at least one vinylgroup.
 6. The method according to claim 3, wherein the polymerization isoligomerization of the cyclosiloxan compound, thereby forming aninsulation film comprised of oligomers of the cyclosiloxan compound. 7.The method according to claim 2, wherein said silicon-containinghydrocarbon is a cyclosiloxan compound having reactive groups.
 8. Themethod according to claim 7, wherein said reactive group is selectedfrom the group consisting of alkoxy group and vinyl group.
 9. The methodaccording to claim 8, wherein said silicon-containing hydrocarbon hasthe formula (Si_(n)O_(n)R_(2n−m))X_(m,) wherein n is an integer of 3–6,m represents the number of a unsaturated bond between Si and C and is aninteger of 1–6 (m≦n), R is C₁₋₆ saturated or unsaturated hydrocarbonattached to Si, X is —O—C_(p)H_(2p+l) wherein p is an integer of 1–4 or—C_(z)H_(2(z−w)+2) wherein z is an integer of 1–4, and w represents thenumber of unsaturated carbon bonds and is an integer of 1–3.
 10. Themethod according to claim 7, wherein said reactive group is selectedfrom the group consisting of amino group and acid radical.
 11. Themethod according to claim 10, wherein the reactive group is included ina different compound from the silicon-containing hydrocarbon.
 12. Themethod according to claim 10, wherein the reactive group is included inthe silicon-containing hydrocarbon.
 13. The method according to claim 2,wherein said silicon-containing hydrocarbon compound has the formulaSi_(α)O_(α−1)R_(2α−β+2)Xβ wherein α and β are integers of 1–3, R is C₁₋₆hydrocarbon attached to Si, and X is a reactive group.
 14. The methodaccording to claim 13, wherein said reactive group is selected from thegroup consisting of amino group and acid radical.
 15. The methodaccording to claim 13, wherein said reactive group is alkoxy group. 16.The method according to claim 1, wherein the hard film has a dielectricconstant of 3.5 or less.
 17. The method according to claim 1, whereinthe carrier gas is selected from the group consisting of N₂, He, Ne, andAr.
 18. The method according to claim 1, further comprising introducingan additive gas selected from the group consisting of an oxidizing gasand a gas of CxHyOz wherein x=0–3, y=2–15, and z=0–7, into the reactionspace when the source gas is introduced.
 19. The method according toclaim 1, further comprising introducing as an additive gas a gas ofCxHyOz which is selected from the group consisting of H_(2,) C₁₋₆saturated or unsaturated hydrocarbon, C₁₋₆ alkanol, and C₃₋₂₀ ether intothe reaction space when the source gas is introduced.
 20. The methodaccording to claim 1, wherein the low-frequency RF power is 1%–50% ofthe high-frequency RF power.
 21. The method according to claim 1,wherein the low-frequency RF power has a frequency of 2 MHz or less. 22.A method for forming a hard film on an insulation film formed on asemiconductor substrate by plasma reaction, comprising the steps of:forming an insulation film on a semiconductor substrate placed in areaction space by plasma polymerization using a silicon-containinghydrocarbon compound; vaporizing a silicon-containing hydrocarboncompound to provide a source gas, said silicon-containing hydrocarboncompound comprising a cyclic Si-containing hydrocarbon compound and/or alinear Si-containing hydrocarbon compound, as a basal structure, withreactive groups for forming oligomers using the basal structure;introducing a reaction gas comprising the source gas and a carrier gasinto the reaction space; and forming a hard film on the insulation filmby activating plasma polymerization reaction using a combination oflow-frequency RF power and high-frequency RF power in the reactionspace, wherein the plasma polymerization reaction is activated whilecontrolling the flow of the reaction gas to lengthen a residence time,Rt, of the reaction gas in the reaction space, wherein 100 msec≦Rt,Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r _(w) ² d/F wherein: Pr: reaction spacepressure (Pa) Ps: standard atmospheric pressure (Pa) Tr: averagetemperature of the reaction (K) Ts: standard temperature (K) r_(w):radius of the silicon substrate (m) d: space between the siliconsubstrate and the upper electrode (m) F: total flow volume of thereaction gas (sccm).
 23. The method according to claim 22, wherein thesilicon-containing hydrocarbon used for forming the hard film and thesilicon-containing hydrocarbon used for forming the insulation film havethe same chemical formula.
 24. The method according to claim 22, whereinthe formation of the insulation film and the formation of the hard filmare conducted continuously in the reaction space.
 25. A method forforming a hard film on an insulation film formed on a semiconductorsubstrate by plasma reaction, comprising the steps of: vaporizing asilicon-containing hydrocarbon compound to provide a source gas, saidsilicon-containing hydrocarbon compound comprising a cyclicSi-containing hydrocarbon compound and/or a linear Si-containinghydrocarbon compound, as a basal structure, with reactive groups forforming oligomers using the basal structure; introducing a reaction gascomprising the source gas and an additive gas into a reaction space forplasma CVD processing wherein a semiconductor substrate on which aninsulation film is formed is placed, said additive gas being selectedfrom the group consisting of C₁₋₆ saturated or unsaturated hydrocarbon,C₁₋₆ alkanol, and C₃₋₂₀ ether; and forming a hard film on the insulationfilm by activating plasma polymerization reaction using radio-frequencyRF power in the reaction space, wherein the plasma polymerizationreaction is activated while controlling the flow of the reaction gas tolengthen a residence time, Rt, of the reaction gas in the reactionspace, wherein 100 msec ≦Rt,Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r _(w) ² d/F wherein: Pr: reaction spacepressure (Pa) Ps: standard atmospheric pressure (Pa) Tr: averagetemperature of the reaction (K) Ts: standard temperature (K) r_(w):radius of the silicon substrate (m) d: space between the siliconsubstrate and the upper electrode (m) F: total flow volume of thereaction gas (sccm).
 26. The method according to claim 25, wherein thereaction gas further comprises a carrier gas.
 27. The method accordingto claim 25, wherein the radio-frequency RF power is comprised of 1%–50%of low-frequency RF power and 50%–99% of high-frequency RF power.
 28. Amethod for forming a hard film on an insulation film formed on asemiconductor substrate by plasma reaction, comprising the steps of:vaporizing a silicon-containing hydrocarbon compound to provide a sourcegas, said silicon-containing hydrocarbon compound comprising a cyclicSi-containing hydrocarbon compound and/or a linear Si-containinghydrocarbon compound, as a basal structure, with reactive groups forforming oligomers using the basal structure; introducing a reaction gascomprising the source gas into a reaction space for plasma CVDprocessing wherein a semiconductor substrate on which an insulation filmis formed is placed; and forming a hard film on the insulation film byactivating plasma polymerization reaction using radio-frequency RF powerin the reaction space, wherein the plasma polymerization reaction isactivated while controlling the flow of the reaction gas to lengthen aresidence time, Rt, of the reaction gas in the reaction space, wherein100 msec ≦Rt,Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r _(w) ² d/F wherein: Pr: reaction spacepressure (Pa) Ps: standard atmospheric pressure (Pa) Tr: averagetemperature of the reaction (K) Ts: standard temperature (K) r_(w):radius of the silicon substrate (m) d: space between the siliconsubstrate and the upper electrode (m) F: total flow volume of thereaction gas (sccm).
 29. The method according to claim 27, wherein thereaction gas further comprises the gas of CxHyOz which is selected fromthe group consisting of C₁₋₆ saturated or unsaturated hydrocarbon, C₁₋₆alkanol, and C₃₋₂₀ ether.
 30. The method according to claim 27, whereinthe reaction gas further comprises a carrier gas.
 31. The methodaccording to claim 27, wherein the radio-frequency RF power is comprisedof 1%–50% of low-frequency RF power and 50%–99% of high-frequency RFpower.